Holographic Dark Energy from a Polynomial Expansion in the Hubble Parameter

Abstract: This work investigates a generalized holographic dark energy (HDE) model defined by a polynomial expansion in the Hubble parameter, incorporating the first three leading terms proportional to $H^{2}$, $H^{4}$, and $H^{6}$ through a variable parameter in the expression for the energy density. The analysis is developed within the framework of a spatially flat Friedmann-Lema^itre-Robertson-Walker (FLRW) Universe composed of non-interacting matter and this HDE fluid. We derive the complete set of Friedmann equations to study the cosmic evolution and subsequently examine the system for the existence of thermodynamic $P-V$ type phase transitions. Finally, a comprehensive comparison with the predictions of the standard $\Lambda$CDM model is presented.